[Patent Literature 1] JP 2005-86692 A
For example, Patent Literature 1 discloses a gateway apparatus that permits an in-vehicle instrument connected to a first network to activate in-vehicle instruments, which are connected to a different second network, from sleep state without delay. This gateway apparatus connects the first network and the second network to each other using a signal line having a switch; the signal line connects (i) a signal transmission route between the bus of the first network and a transceiver and (ii) a signal transmission route between the bus of the second network and a transceiver. When the gateway apparatus is in the sleep state, the switch of the signal line is closed to connect the buses of the different first and second networks via the signal line. Therefore, a wake-up signal is transmitted in the first network, the wake-up signal can be transferred to the different second network, without waiting for activation of the gateway apparatus.
In a general communication system, the increase of the number of communication nodes connected to a single network causes the increase in stray capacitance, or the reflection of signals due to impedance mismatching; this distorts or declines the waveforms of signals in the network bus, tending to cause a transmission error. Such issue eventually limits the number of communication nodes connected to a single network. If the number of communication nodes intended to be networked exceeds the limit number of a single network, a different second network is additionally prepared and connected to the first network via a gateway apparatus.
Patent Literature 1 describes the configuration of the gateway apparatus in which the different networks are mutually connected directly using a switch as if a new temporal single network is produced by connecting all the different networks. This new temporal single network apparently contains the whole of the communication nodes belonging to all the different networks. This may cause a transmission error of a wake-up signal in the new temporal single network having a great number of communication nodes to lead to the possibility that a communication node belong to a first network cannot activate certainly communication nodes belonging to a different second network.